The loads on a component can be decomposed into those that are axial, those that exert bending moments and those that exert torques. One of these usually dominates to such an extent that structural elements are specially designed to carry it, and these have common names. Thus ties carry tensile loads; beams carry bending moments; shafts carry torques; columns carry compressive axial loads. Figure 11.3 shows these modes of loading applied to shapes that resist them well. The point it makes is that the best material-and-shape combination depends on the mode of loading. In what follows, we separate the modes, dealing with each separately.
In axial tension, the area of the cross-section is important but its shape is not: all sections with the same area will carry the same load. Not so in bending: beams with hollow-box or I-sections are better than solid sections of the same cross-sectional area. Torsion too, has its efficient shapes: circular tubes, for instance, are more efficient than either solid sections or I-sections. To characterize this we need a metric—a way of measuring the structural efficiency of a section shape, independent of the material of which it is made. An obvious one is that given by the ratio of the stiffness or strength of the shaped section to that of a ‘neutral’ reference shape, which we take to be that of a solid square section with the same cross-sectional area, and thus the same mass per unit length, as the shaped section
المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .
|